Development of time-independent eigenstate-free methods for calculating vibronic spectra beyond the harmonic approximation
Final Report Abstract
A Raman wavefunction program for the accurate calculation of vibronic spectra beyond the harmonic and the Franck-Condon approximations has been developed, which allows for the investigation of photoelectron spectra with a high density of states. The prevention of any sumover-states steps within the formalism allows to deal very efficiently with spectral regions, in which individual state identities are lost. A series of technical refinements has been used to reduce memory requirements and computation times. An analysis of the vibronic spectra became feasible due to our residual-based algorithm for the calulation of eigenpairs (RACE). This allows to identify the dominant progressions, which is necessary for a detailed understanding of the spectra. An optimization of the modal basis for each spectral point of a vibronic spectrum has been implemented, but no significant advantages by its use could be found. Therefore, modal-optimized algorithms cannot be advocated within the context of the calculation of photoelectron spectra. The new Raman wavefunction program has been used to study the X̃ 2A2←X̃ 1A1 photoionization spectrum of furan and the S1 ← S0 vibronic absorption spectrum of formaldehyde. The latter rquired the implementation of Herzberg-Teller terms into the program and vibrational angular momentum terms were found to be very important for this double-well system. Excellent agreement with experimental results was obtained in both cases. Remaining deficiencies in the agreement originate mainly from limitations in the electronic structure calculations or the multidimensional potential energy surfaces in general rather than the vibrational structure calculations.
Publications
- Refined analysis of the X̃ 2A2←X̃ 1A1 photoelectron spectrum of furan. J. Chem. Phys. 148, 054306 (2018)
T. Petrenko and G. Rauhut, J.
(See online at https://doi.org/10.1063/1.5018928) - Modal optimisation within the time-independent eigenstate-fee Raman wavefunction formalism. Mol. Phys.
T. Petrenko and G. Rauhut
(See online at https://doi.org/10.1080/00268976.2019.1643047) - Account of non-Condon effects in time-independent Raman wavefunction theory: Calculation of the S1 ←−S0 vibronic absorption spectrum of formaldehyde. J. Chem. Phys. 152, 114109 (2020)
T. Petrenko and G. Rauhut
(See online at https://doi.org/10.1063/5.0003272)
